Before You Start

Before you begin setting up your replication site, there are several items that you need to verify:

• Ensure that GLOBAL_NAMES is set to TRUE in your initialization parameter file.

• Ensure that you have allocated enough job processes at each master site.

Global Names

To ensure that your replicated environment works properly, you must set the GLOBAL_NAMES initialization parameter in the initialization parameter file to TRUE. The following description and setting are in your initialization parameter file:

# Global Naming -- enforce that a dblink has same name as the db it connects to
global_names = TRUE

This initialization parameter must be set to TRUE for each database that is participating in your replicated environment, including both master and snapshot sites.

Job Processes

It is important that you have allocated sufficient job processes, sometimes referred to as SNP background processes, to handle the automation of your replicated environment. That is, automatically propagating the deferred transaction queue, purging the deferred transaction queue, refreshing snapshots, and so on.

For multimaster replication, each site has a scheduled link to each of the other master sites. For example, if you have six master sites, each site has scheduled links to the other five sites. You typically need one process for each scheduled link. You may also want to add an additional job process for purging the deferred transaction queue and other user-defined jobs.

By the nature of snapshot replication, each snapshot site typically has one scheduled link to the master database and requires at least one job process. Snapshot sites typically require between one and three job processes, depending on purge scheduling, user-defined jobs, and the scheduled link. Alternatively, if your users are responsible for manually refreshing the snapshot through an application interface, you do not need to create a scheduled link and your snapshot site requires one less job process.

In addition to defining the number of job processes, you must also define the job interval. The job interval determines how often your job processes "wake up" to execute any pending operations, such as pushing a queue. While the default value of 60 seconds is adequate for most replicated environments, you may need to adjust this value to maximize performance for you individual requirements. For example, if you want to propagate changes every 20 seconds, a job interval of 60 seconds would not be sufficient. On the other hand, if you need to propagate your changes once a day, you may only want your SNP process to check for a pending operation once an hour.

The job processes are also defined in the initialization parameter file, usually under the "Oracle replication" heading.

job_queue_processes = 7
job_queue_interval = 60

After you have modified the contents of your initialization parameter file, restart your database with these new settings.

See Also: Chapter 7, "Planning Your Replication Environment" in Oracle8i Replication for more information about the initialization parameters that are important for Oracle replication, and see the Oracle8i Administrator's Guide for information on restarting your database.